Gas turbine compressor spools can oscillate axially in harmony with a pressure pulse generated in the gas path, with a relatively low frequency noise resulting (e.g. 100-400 Hz). The pressure pulse in the gas path may be caused by any of the combustion system, compressor blade row rotating stall, and mild surging of a compressor stage. The varying pressure causes fluctuations of the axial load on the turbine blades and disks of the compressor. Depending on the axial stiffness of the thrust bearing support connected to the casing of the gas turbine engine, the axial movement of the rotor spool can fall in phase with the source of the pressure pulse, potentially producing a relatively loud noise.
Accordingly, there is a need to provide an improved axial damping of rotor spool oscillations.